An increase in 18F-fluorodeoxyglucose (FDG) uptake in an asynergic region with reduced blood flow provides a metabolic signal for viable myocardium, capable of improving after revascularization. In the current study, we determined whether the magnitude of reduction in regional blood flow and FDG in asynergic regions can also discriminate viable from nonviable myocardium. We studied 95 regions in 7 patients with chronic coronary artery disease who underwent pre-revascularization PET at rest with FDG and 15O-water and pre- and post-revascularization gated magnetic resonance imaging (MRI) and radionuclide angiography. Mean left ventricular ejection fraction increased from 30 + 13% pre- revascularization to 35 + 11% post-revascularization. An average of 2-4 MRI and PET transaxial slices were matched and analyzed per patient. For each slice, pre- and post-revascularization systolic wall thickening was assessed in 5 regions by MRI. Pre-revascularization, systolic wall thickening was absent in 25 of 95 (26%) regions. Post- revascularization, systolic wall thickening improved in 9 (36%) regions and remained abnormal in 16 (64%). Mean regional blood flow was similar in regions that improved post-revascularization (0.80 + 0.17 ml/g/min) compared to regions that did not improve post-revascularization (0.71 + 0.26 ml/g/min, p=NS). However, mean FDG uptake was significantly higher in asynergic regions that improved post-revascularization (0.94 + 0.25) when compared to regions with absence of systolic wall thickening post-revascularization (0.61 + 0.23, p<0.003). These data indicate that reliance on the magnitude of net transmural blood flow of 15O-water is insufficient for predicting recovery of function after revascularization. On the other hand, metabolic assessment with FDG in asynergic regions provides unique insights into myocardial viability.